You're right in your observations. Things have changed quite a bit from the 1980s and even from the 1990s to today. In the past, a more conservative approach to ACL rehab was the norm.
Patients were immobilized in a cast for sic to eight weeks. That was followed by crutches for another eight to 10 or 12 weeks. Today's rehab is more "functional." In other words: get them back on their feet doing everyday activities as soon as possible.
Motion right away and putting weight through the joint are the focus of rehab now. Proprioception training is also a key feature. Proprioception is the awareness of the joint, its position, and movement through its range of motion.